The ADvanced Systems Laboratory (ADSL)
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Journal-guided Resynchronization for Software RAID
Timothy E. Denehy,
Andrea C. Arpaci-Dusseau,
Remzi H. Arpaci-Dusseau
Department of Computer Sciences
,
University of Wisconsin-Madison
Abstract:
We investigate the problem of slow, scan-based, software RAID resynchronization that restores consistency after a system crash. Instead of augmenting the RAID layer to quicken the process, we leverage the functionality present in a journaling file system. We analyze Linux ext3 and introduce a new mode of operation, declared mode, that guarantees to provide a record of all outstanding writes in case of a crash. To utilize this information, we augment the software RAID interface with a verify read request, which repairs the redundant information for a block. The combination of these features allows us to provide fast, journal-guided resynchronization. We evaluate the effect of journal-guided resynchronization and find that it provides improved software RAID reliability and availability after a crash, while suffering little performance loss during normal operation.
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